Preparation of alpha-monochloro acids

ABSTRACT

ALKANEMONOCARBOXYLIC ACIDS AND CYCLOALKANECARBOXYLIC ACIDS ARE CHLORINATED IN THE PRESENCE OF A CHLORINATION CATALYST TO OBTAIN HIGH YIELDS OF THE CORRESPONGING ALPHAMONOCHLORO ACID WHEN THE REACTION IS CARRIED OUT AT 145200*C.

United States Patent PREPARATION OF ALPHA-MONOCHLORO ACIDS Arthur R.Sexton and John C. Little, Midland, Mich., as-

signors to The Dow Chemical Company, Midland, Mich.

No Drawing. Continuation-impart of application Ser. No. 346,400, Feb.21, 1964. This application June 19, 1967, Ser. No. 647,181

Int. Cl. C07c 61/08 US. Cl. 260-514 6 Claims ABSTRACT OF THE DISCLOSUREAlkanemonocarboxylic acids and cycloalkanecarboxylic acids arechlorinated in the presence of a chlorination catalyst to obtain highyields of the corresponding alphamonochloro acid when the reaction iscarried out at 145- 200 C.

This is a continuation-in-part of copending application Ser. No. 346,400filed Feb. 21, 1964, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to an improvedchlorination process which provides unexpectedly high yields of certainalpha-monochloroalkanecarboxylic acidsalpha-monochloro-cycloalkanecarboxylic acids at high levels ofconversion.

The uncatalyzed chlorination of alkanemonocarboxylic acids andcycloalkanemonocarboxylic acids produces mixtures of randomlychlorinated acids from which it is impossible to separate a good yieldof the alpha-chloro isomer. It is known that alkanecarboxylic acids canbe chlorinated in the presence of various acidic inorganic catalysts toobtain predominantly the alpha-chloro derivative. An acyl halide formspart of the catalyst system and is apparently an essential component.This may be added separately or formed in situ from the unchlorinatedacid reactant. Known inorganic acid catalysts include the halides,oxyhalides, oxygen acids, and oxides of phosphorus, arsenic, antimony,sulfur, selenium, and tellurium; the halides of tin, iron, and aluminum;the halooxygen acids of phosphorus and sulfur; and the essentialequivalents of these, for example, elemental phosphorus plus iodine,iron filings, and the like. This process is recommended to be carriedout at 50-140 C., preferably at 90-100 C.

Similarly, it is known that acids such as cyclohexanecarboxylic acid canbe chlorinated at about the same temperature and in the presence of thesame kind of catalyst to obtain improved yields of the alphachloroderivatives.

Both of the above known procedures provide somewhat improved yields ofthe desired alpha-monochlorinated products. For example, very highyields of alpha-chloropropionic acid are thereby obtained. Somewhatlower yields of alpha-chloro higher aliphatic acids are found. It hadbeen thought that such processes also provided high yields of thealpha-chloro acid when cyclohexanecarboxylic acid was chlorinated.However, more recent work using modern analytical techniques hasindicated that the actual yields of a-chloro isomers when theseprocesses are applied to such acids are substantially lower thanpreviously thought and that appreciable quantities of the undesirablerandomly chlorinated isomers are in fact present in the chlorinatedproducts.

SUMMARY OF THE INVENTION It has now been found that a near quantitativeyield of the alpha-chloro acid is obtained when an alkanemonocarboxylicacid or a cycloalkanemonocarboxylic acid as defined below is chlorinatedin the liquid phase in the presence of an inorganic acid catalyst asdescribed above and- 3,584,036 Patented June 8, 1971 DETAILEDDESCRIPTION The present improved process is applicable to making thealpha-monochloro derivatives of alkanecarboxylic acids of 4-18 carbonatoms, particularly those having the general formula wherein R is analkyl radical of 1-16 carbon atoms and R is hydrogen or an alkyl radicalof 1-8 carbon atoms. Acids of the above formula where R is primary alkylof 2-16 carbon atoms and R is hydrogen are preferred reactauts.

The improved process is similarly adapted to making the alpha-monochloroderivatives of cycloalkanemonocarboxylic acids of 5-7 carbon atoms suchas cyclobutanecarboxylic acid, cyclopentanecarboxylic acid, andcyclohexanecarboxylic acid. Acids of the first defined class includebutyric acid, hexanoic acid, octanoic acid, lauric acid, and stearicacid.

Catalysts which can be employed in the present improved process arethose previously known for the general reaction as defined above. Thesemay be used in combination with an acyl halide or carboxylic acidanhydride as taught by the prior art, either such a derivative ofanother carboxylic acid or, preferably, the halide or anhydride of theacid being chlorinated. The quantity of inorganic catalyst is notcritical so long as it is at least a catalytically effective amount.Catalyst concentrations of 0.1-5 percent by weight of carboxylic acidare suitable and 0.5-2 percent is preferred.

The reaction can be carried out using any of a number of knownchlorinating agents, for example, chlorine, N- chlorosuccinimide,N-chlorourea, phosphorus pentachloride, sulfuryl chloride, or the like.Gaseous chlorine is preferred as a convenient and economical reagent andfor the simplified separation procedures required to obtain a pureproduct.

The quantity of chlorinating agent is not a critical limitation in theprocess for, as shown in prior art processes, an amount considerablyless than or in excess of that theoretically needed to monochlorinateall of the carboxylic acid can be used successfully. Preferably, no morethan about 130 percent of the theoretical quantity is used in order toavoid excessive formation of polychlorinated acid. Best yields of thealpha-monochloro acid are obtained using -120 percent of the theoreticalproportion of chlorinating agent.

The liquid phase in which the acid is chlorinated may consistessentially of the liquid carboxylic acid or a solvent suitable for thiskind of chlorination reaction may be included. Chlorinated ornitro-substituted aromatic or aliphatic hydrocarbons such astetrachloroethane, dichlorobenzene, nitrobenzene, and trichlorobenzenecan be used as solvents. Where the normal boiling point of the solventsis below the reaction temperature, the reaction must be run undersuperatmospheric pressures. Operation in the absence of a solvent ispreferred.

In a preferred mode of operation of this improved process, chlorine isbubbled through a mole of molten carboxylic acid containing 0.5-2% byweight of phosphorus trichloride until 0.8-1.2 moles of chlorine havebeen reacted as measured by the gain in weight of the reaction mixture,the temperature of the mixture being maintained throughout at 155-l95 C.The crude reaction mixture thereby obtained consists essentially of thealpha-monochlorocarboxylic acid and a minor proportion of unreactedacid, together with catalyst residues and other chlorinated acids whichare usually present in amounts of the order of tenths of a percent byweight. Further purification, where desirable, can be accomplished byknown means, for example, crystallization, distillation, orchromatographic absorption.

The major present use for alpha-monochlorocarboxylic acids of theclasses described is as chemical intermediates and the reaction productsobtained from the claimed process are ordinarily of sufficiently highpurity to be used directly for such purpose with no intermediatepurification or with only a flash distillation to remove the traces ofcatalyst residues and polychlorinated byproducts. Since randomlychlorinated carboxylic acid isomers are not readily separated and arealso relatively easily dehydrohalogenated, the advantage of the presentprocess in providing a product which can be used in this fashion withoutneed for fractional distillation or other extended purificationprocedure is apparent. The importance of the high conversions and,particularly, the high yields which are characteristic of the claimedprocess is thereby emphasized.

The new process and its advantages and differences from the knownmethods are illustrated by the examples which follow.

EXAMPLE 1 A cylindrical reactor equipped with a perforated ring spargerat the bottom, reflux condenser, and temperature regulating andmeasuring means was charged with 353 g. of butyric acid and 11 g. ofphosphorus trichloride. This mixture was reacted with 319 g. of chlorineintroduced through the sparger at ISO-180 C. over a period of 8 hours.The organic product contained 92.2 percent by weight of 2-chlorobutyricacid, 2.3 percent of 2,2-dichlorobutyric acid, 2.1 percent of unreactedbutyric acid, and the remainder was other chlorinated products.

EXAMPLE 2 By the procedure of Example 1, a mixture of 70 g. of hexanoicacid and 1.53 g. of P001 was reacted with 53 g. of chlorine at 175 C. in3 hours. The organic reaction product contained 94.5 percent by weightof 2-chlorohexanoic acid with the remainder being other chlorinatedproducts. This represented a yield of 94.5 percent of the alpha-chloroacid based on 100% conversion.

When the above procedure is repeated excepting for holding thetemperature below 150, the yield is reduced to 25-70%.

EXAMPLES 3-9 Using the apparatus and general procedure of Example 1,hexanoic acid was reacted with about 1.1 mole equivalents of chlorinewith various catalysts and temperatures as noted. Yields listed are of2-chloro-hexanoic acid and are calculated as in previous examples.Reaction times were 3-5 hours.

Temp Percent Percent Ex-. Catalyst conversion yield 4 P+I2 175 88 90 5PzO5+HCL 175 85 U2 6 Hexanoyl chl0ride+HzSO4 125 77 35 7.. Same 150 7872 8 Same 175 00 94 9 None 175 61 50 Examples 6-8 show the increasedconversion and yield of alpha-chloro acid as the temperature isincreased to the preferred range.

EXAMPLE 10 To a 50 ml. tapered flask equipped with condenser and spargerand immersed in an oil bath maintained at 175 C. there was added 5.0 g.of cyclobutanecarboxylic acid and 0.45 g. of phosphorus trichloride.With the contents of the flask held at 175 C. by the oil bath, 1.8 g. ofchlorine was added through the sparger over a period of 2.3 hours.Analysis of the organic reaction product showed it to consist of 39.8percent by weight of l-chlorocyclobutanecarboxylic acid, and 3.3 percentof other chlorinated acids, the balance being cyclobutanecarboxylicacid. The yield of tat-chlorinated acid was 92 percent based on thecyclobutanecarboxylic acid disappearing.

EXAMPLES l 1-l7 A glass reactor flask equipped with stirrer, condenser,sparger, and means for controlling and measuring temperature was chargedwith 256 g. of cyclohexanecarboxylic acid and 8 g. of phosphorustrichloride. The temperature of the mixture was adjusted to about 100 C.and 142 g. of chlorine was introduced through the sparger over a periodof about 6 hours at 97101 C. Analysis of the organic portion of thereaction mixture showed it to contain 29 weight percent of unreactedcyclohexanecarboxylic acid, 12 percent of 1-chlorocyclohexanecarboxylicacid, 50 percent of isomeric monochlorocyclohexanecarboxylic acids, andthe remainder was polychlorinated products. The yield of1-ch1orocyclohexanecarboxylic acid was 18 percent based on thecyclohexanecarboxylic acid which was actually reacted.

Using essentially the same procedure except for immaterial variations incatalyst concentration as noted, chlorinations were carried out atvarious temperatures with the same proportion of reactants. The resultsare summarized in the following table wherein the listed yields are of1-chlorocyclohexanecanboxylic acid.

TABLE Temp., Wt. percent Percent Percent Example 0. P013 conversionyield EXAMPLES 18-20 Cyclohexanecarboxylic acid was reacted withchlorine at a constant temperature of 170 C. and with variousproportions of PCl under conditions otherwise as described in Example12. The yield of the 1-chloro acid was found to be little affected bythe changes in catalyst concentration as shown below, but the color ofthe product increased somewhat with the concentration of catalyst.

Wt. percent PCI 0.6, 1.0, 2.0. Percent yield: 99, 98.5, 96.5.

6 4. The process of claim 1 wherein the acid is cyclo- References Citedhexanecarboxyhc acid.

5. The process of claim 1 wherein the chlorinating agent UNITED STATESPATENTS is chlorine. 3,052,716 9/1962 Jason et al 260514 6. The processof claim 1 wherein the chlorination 5 catalyst is a. halide, oxyhalide,oxygen acid, or oxide of CHARLES B. PARKER, Primary Examiner phosphorus,arsenic, antimony, sulfur, selenium, or tellurium; a halide of tin, ironor aluminum; a halooxygen acid KILLOS Asslstant Exammer of phosphorus orsulfur; phosphorus plus iodine; or a US. Cl. X.R.

combination thereof. 10 260-413, 539

